Hydrogenated block copolymers such as polystyrenepoly(ethylene-co-butylene)-polystyrene (SEBS) block copolymers are important thermoplastic elastomers. Unfortunately the utility at elevated temperatures is limited by the relatively low glass temperature (Tg) of the polystyrene end segments. Typical SEBS block copolymers lose most of their reinforcing ability above 60.degree.-70.degree. C., even though the Tg of the polystyrene segments is 100.degree. C. A few attempts have been made to improve the performance of SEBS block copolymers by chemical modification, but the vast opportunities that are available to do this have scarcely been investigated.
Benzoylation of SEBS block copolymers has been attempted. Benzoylation of the polystyrene segments in these copolymers did not raise their glass transition temperatures sufficiently so that the polymers would be useful above at least 100.degree. C. These polymers are not able to be employed in medical applications where sterilization is important. Automotive and adhesive applications where strength at high temperature is important are also not possible. It is therefore an object of this invention to provide SEBS block copolymers which are useful above 100.degree. C.